1. Field of the Invention
The present invention relates to an image processing method for processing an image of a ground surface which is detected by a line sensor installed on a flight vehicle.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2003-83745 discloses an aerial triangulation using an image photographed from a flight vehicle (e.g. airplane, satellite). According to the document, a configuration is as follows. That is, an image obtained by three line sensors and position/posture information of a camera detected by a gyroscope, an inertial navigation device and a GPS satellite are recorded in recording means in a interrelated manner. The position/posture information of a camera is corrected by reducing a deviation between spatial position information corresponding to a reference point on a ground surface and an observation position which is obtained from the image and the position/posture information of a camera recorded in the recording means.
However, such technology above-described has a following problem. Referring to FIG. 1, a line sensor which continuously obtains a one-dimensional image and is installed in a flight vehicle (e.g. airplane, satellite, etc.) photographs a surface of the earth while flying (hereinafter, a two-dimensional image obtained by such photographing is referred to as “line sensor image”).
A line 02 of a line sensor image 01 is an image of a photographing area 09 on a ground surface 11 which is photographed, within a sensor view 07, from a flight position 05 on a flight path 04 of a flight vehicle 100. Also, a line 03 is an image of a photographing area 10 on the ground surface 11 which is photographed from a flight position 06.
On the other hand, referring to FIG. 2, an area sensor (i.e. frame sensor) installed in a flight vehicle photographs a surface of the earth while flying (hereinafter, a two-dimensional image obtained by such photographing is referred to as “area sensor image”). An area sensor image 12 is obtained by photographing a photographing area 15 on the ground surface 11, within a sensor view 14, from a flight position 13 on a flight path 04. Therefore, the area sensor image 12 is an image of a surface of the earth which is photographed within a larger sensor view than the sensor view 07 of a line sensor image shown in FIG. 1.
Here, when a survey is performed, a located position of a point 08 whose three-dimensional position is known (hereinafter, referred to as “point P”) in an image has to be identified. When the same area is photographed using an area sensor and a line sensor, a number of photographing times of an area sensor is smaller than that of a line sensor. Therefore, the identification of a position of the point P 08 in a line sensor image is difficult than the identification of a position of the point P 08 in an area sensor image.
In a case of a line sensor image, information associated with an image of the line 02 shown in FIG. 1 such as a photographing clock time, a flight position and a photographing posture differs from that of the line 03. Therefore, it is difficult to specify a line number and a column number (hereinafter, referred to as “image coordinates”) of a point at which the point P 08 is photographed in a line sensor image 01. It is impossible to keep information of a flight position and a photographing posture with respect to all lines of the line sensor image 01.
On the other hand, in a case of an area sensor image, as shown in FIG. 2, the same flight position and photographing posture data can be applied to an image in the sensor field of view 14. Therefore, identifying a position of the point P 08 in a line sensor image is difficult in comparison with identifying a position of the point P 08 in an area sensor image.
As mentioned above, there is a problem of which a calculation of image coordinates of a pixel corresponding to the point P 08 using a line sensor image is difficult in comparison with that using an area sensor image.